Thermal-mechanically processed low-alloy steel

ABSTRACT

Disclosed is a low carbon-low alloy content steel which is highly responsive to thermal-mechanical processing with air hardening capability. The steel is compatible process-wise with typical tool steels useful in the impact layer of armor. The alloy steel of this invention yields a high toughness material useful as the backing material for the impact layer of armor.

United States Patent 11 1 UNITED STATES PATENTS 8/1943 Bagsar 75/128 w Briggs 1 Aug. 7, 1973 [5 1 THERMAL-MECHANICALLY PROCESSED 3,164,495 1/l965 Furgason 75/123 w LOW ALLOY STEEL 3,615,879 l0/l97l Herzog 75/l28 W [75] Inventor: Bill N. Briggs, Santa Ana, Calif.

. Primary Examiner-L. Dewayne Rutledge [73] Asslgnee' r g 'lz gs is s txgg i Assislq tt Examiner- -w. R. Satterfield V V A y, Washington, DC. itgrney-Harry M. Saragoynz, Edward J. Kelly [22] Filed: Apr. 26, 1972 [21] Appl. No 247,643 [57] ABSTRACT Disclosed is a low carbon-low alloy content steel which v [52] US. Cl. 148/36, 75/128 W is g y responsive to thermaLmechanical processing [5] l llll. CL... C22C 29/00, C22C 39/20 with air hardening capabimy The stee| is compatime [58] held 0 Search 75/28 W, l28 Y, process wise with ypi tool steels useful in the 75/,26 C1 126 E; 148/36 pact layer of armor. The alloy steel of this invention yields a high toughness material useful as the backing [56] References cued material for the impact layer of armor.

3 Claims, No Drawings THERMAL-MECHANICALLY PROCESSED LOW-ALLOY STEEL This is a division of application Ser. No. 143,232, filed May 13,1971.

BACKGROUND OF THE INVENTION Armor steel requirements establish that a high hardness steel is needed to be effective in breaking up armor piercing projectiles. To prevent shattering of the armor a high toughness is required. Thus, a certain hardness and toughness of the armor is a requirement.

Earlier approaches to making armor material has included processing a homogeneous material in attempts to produce high strength material while retaining toughness in the material. Later conclusions drawn from earlier testing has indicated that a homogeneous steel panel when processed to yield sufficient hardness to break up a projectile generally results in panel shattering which defeats usefulness for multiple hit capability.

Recently, steels of high alloy content have been pro vided which steels have been used in combinations to provide a high hardness impact layer of armor with a lower hardness backup layer of armor. The steels having the necessary hardness and toughness have not been metallurgically compatible, i.e., achieve optimum properties under the same processing parameters. The cost of the alloys has been higher due to higher alloy content and special processing conditions necessary due to the metallurgical incompatibility of the alloys.

An object of this invention is to provide a steel alloy composition which is metallurgically compatible with a steel used for the impact layer of armor.

Another object is to provide a steel lower in alloy content which can be processed to yield a lower hardness and higher toughness for the backup layer as compared with the steel used for the impact layer.

SUMMARY OF THE INVENTION A steel alloyprepared by consumable arc vacuum melt technique, and having the nominal chemistry set forth below in Table I, imparts improved performance for the backup alloy of steel armor when thermalmechanically processed as later herein described.

DESCRIPTION OF THE PREFERRED EMBODIMENT The steel alloy of this invention has the nominal chemistry in weight percent as set forth hereinbelow under heading Alloy ADPX-27."

ALLOY ADPX-27 NOMINAL COMPOSITION Mn Si Cr 0.65 0.25 1.00

The above steel alloy is processed by hot rolling at about 2,000F and air cooled. After rolling and air cooling the steel is austenitized at 1900F 1 hr/inch thickness, thermal-mechanically processed 50 percent over a falling temperature range of approximately l500-l200F, 'oil quenched and tempered at a selected tempering temperature from about 400F to about 1050F for about 2 hours to result in a hardness in the range of about 50-55 R, (Rockwell c" scale). The alloy when processed as described yields a Charpy Impact Energy value exceeding 40 ft-lbs. Testspecimens were tested at F in accordance with Watertown Arsenal Laboratory 112/89 (REV). For additional information on testing refer to: Impact Testing No. 1, Calibration of the Charpy Impact Machine and Procedures for Inspection and Testing of Charpy V- Notch Impact Speciments, Watertown Arsenal Laboratory, dated November 1958.

The merit ratings of alloy ADPX-27 were established by testing with an impact alloy of 5% chromiu'm, 1% molybdenum, 1% silicon, and 0.40% carbon and an impact alloy of chromium 1.00%, molybdenum 2.00, silicon 0.40%, carbon 0.44%, manganese 0.72%, nickel 0.60% and vanadium 0.50%. In either combination a merit rating (e.g., respective to performance as an armor) up to 10% greater is obtained. In addition the mechanical properties of alloy ADPX-27 have proven to be outstanding, exhibiting both greater strength and toughness when tempered at either 400F'or 1050F than a commercially utilized backup alloy steel, HP 9-4-30, having a nominal chemistry of nickel 9%, cobalt 4%, chromium 1%, molybdenum 1%, and carbon 0.30%.

The advantages of alloy ADPX-27 over the prior art alloy similarly used are:

1. More economical to produce and to process into armor.

2. Metallurgically compatible with alloy steel used for impact layer of armor which permits processing together.

3. Provides a tougher and mechanically stronger backup panel for impact layer alloy.

4. Has greater response to thermal-mechanical processing (e.g., yields a hardness of 4-6 points R greater than the value obtained in the conventionally heat treated condition).

The nickel content may be decreased to as low as 2 percent when adequate carbon, molybdenum and chromiumv are present to achieve hardenability and strength required in a particular use. Steel having about 2 -to about 3.5 percent by weight nickel is the preferred range.

The steel alloy of this invention is air hardening, as is true of prior art steel HP 9-4-.30, which renders this alloy steel accessible to production methods.

The steel alloy of this invention is improved in ballistic performance by surface grinding when used with some composites; however, the alloy chemistry has been shown to be very influential on both decarburization and scale. Chromium content has been shown to significantly reduce decarburization and scale.

The steel alloy of this invention when tempered at about 400F has a tensile strength (KS1) of about 289 whereas the tensile strength of the comparable prior art steel HP 9-4-.30 has a tensile strength of about 275 when tempered at about 400F.

As a result of tests to indicate adequate toughness at the high-hardness levels, an essential quality for an armor backup material, the steel alloy of this invention withstood testing to which the prior art alloy failed. The tests indicate an improvement in the steels capability to rapidly distribute within a test panel both the stress and resulting strain caused by a rapidly applied load.

I claim:

1. A hot rolled and heat treated low carbon-low alloy steel consisting essentially of, in weight percent, about 0.27 carbon, 0.65 manganese, 0.25 silicon, LOO chromium, 2.00 molybdenum, 0.10 vanadium, from about 2.00 to about 3.50 percent nickel, and the balance iron, said steel having been hot rolled at about 2000F, air cooled, and subsequently thermal-mechanically processed by:

a. austenitizing at about 1900F for 1 hour per inch thickness,

b. air cooling to 1500F and holding at said temperature for about 5 minutes,

c. rolling until about 50 percent reduction in thickness is achieved, immediately oil quenching and d. tempering for about 2 hours at a temperature within the range of from about 400F to about 1050F.

2. The low carbon-low alloy content steel of claim I wherein said nominal chemical composition of nickel is about 3.25 percent by weight and said tempering is accomplished at about 400F.

3. The low carbon-low alloy content steel of claim 1 wherein said nominal chemical composition of nickel is about 3.25 percent by weight and said tempering is accomplished at about 1050F. 

2. The low carbon-low alloy content steel of claim 1 wherein said nominal chemical composition of nickel is about 3.25 percent by weight and said tempering is accomplished at about 400*F.
 3. The low carbon-low alloy content steel of claim 1 wherein said nominal chemical composition of nickel is about 3.25 percent by weight and said tempering is accomplished at about 1050*F. 